Such portable electronic instruments as radio receiving sets, tape recorders, etc. are often carried outdoors such as on fishing, swimming, picnics or excursions, and are used on the sea, shore, river, mountain, field, etc. In such cases, if those instruments get wet or humid by rain, sea or river water or spray or are hit by dust, the electronic circuits, speakers or other devices in the instruments are liable to sustain mechanical and electrical troubles.
Nevertheless, if the instruments are tightly covered with ordinary waterproof fabrics or the like, the sounds from the speakers are screened by the covers, and hence, attenuate. Furthermore such covers obstruct free handling of dials, switches, etc., of the instruments.